The model of exocytosis based on the existence of ion channels in the secretory vesicle membrane, that we proposed, was tested at the giant synapse of the squid. The ion-channel-blocking agent nonyl-triethylammonium (9-TEA) was injected directly into the presynaptic nerve terminal in an attempt to inhibit exocytosis. Transmitter release was blocked by 9-TEA but this effect was attributed to a blocking action on calcium channels, invalidating this approach with this compound. Further attempts at this experimental strategy will have to await more specific blocking agents.